Nervous System Notes

Coordinates cellular functions in three basic steps:
- Senses information and sends messages to the central nervous system (CNS).
- Processes and determines appropriate responses based on the received information.
- Issues commands to muscles and organs to carry out the determined responses.

Composed of the brain and spinal cord, which are enclosed in the skull and vertebral column.
Responsible for processing and integrating sensory inputs, as well as coordinating responses.

Composed of nerves leading to and from the CNS, providing pathways for sensory input and motor output.
Divided into two functional divisions:
- Sensory Division: Carries signals from receptors to the CNS regarding environmental changes.
- Motor Division: Carries signals from the CNS to muscles and glands; divided into:
- Somatic Motor Division: Controls voluntary movements of skeletal muscles.
- Autonomic Nervous System (ANS): Controls involuntary responses (smooth muscles, cardiac muscles, glands), further divided into:
  - Sympathetic Division: Prepares the body for action (fight or flight response).
  - Parasympathetic Division: Calms the body, promoting rest and digestion.

Neurons are the main communication cells of the nervous system, with approximately 1 trillion neurons present.
Basic structure includes:
- Neurosoma (cell body): Contains the nucleus and organelles; lacks centrioles, does not undergo mitosis.
- Dendrites: Receive input from neighboring neurons, featuring a branching structure that allows for increased connectivity and information processing.
- Axon: A single extension from the neurosoma that transmits signals to other cells, forming a synapse at the axon terminal.

Multipolar Neurons: Characterized by one axon and multiple dendrites; they are the most common type of neuron.
Bipolar Neurons: Consist of one axon and one dendrite; commonly associated with sense organs.
Unipolar Neurons: Feature one process that leads away from the soma and branches into a T-shape; primarily involved in sensory functions.

Sensory (Afferent) Neurons: Relay sensory information to the CNS; usually classified as unipolar or bipolar.
Interneurons: Process, store, and retrieve information within the CNS; typically multipolar.
Motor (Efferent) Neurons: Conduct signals from the CNS to effectors (muscles and glands); generally multipolar.

Neuroglial cells outnumber neurons at least 10 to 1 and play vital roles in supporting and protecting neurons.

Oligodendrocytes: Form the myelin sheath around CNS axons.
Ependymal Cells: Line brain cavities and produce cerebrospinal fluid (CSF).
Microglia: Function as immune cells that clear debris and pathogens from the CNS.
Astrocytes: Support neurons, maintain the blood-brain barrier (BBB), and regulate blood flow.

Satellite Cells: Provide support and protection for neuron cell bodies.
Schwann Cells: Form the myelin sheath for PNS axons and facilitate regeneration after injury.

Insulates axons, significantly increasing the speed of signal conduction.
Formed by oligodendrocytes in the CNS and Schwann cells in the PNS.
Features a segmented structure with nodes of Ranvier that allows for rapid signal propagation.

White Matter: Composed of myelinated axons; primarily involved in signal transmission.
Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons; largely involved in processing information.

Refers to the charge difference across the neuronal membrane when not stimulated, with the inside of the cell being negative and the outside positive.
Maintained by the sodium-potassium pump, which pumps 3 Na+ ions out and 2 K+ ions in per cycle.

Involves two types of ion channels:
- Ligand-Gated Channels: Open in response to the binding of a specific molecule.
- Voltage-Gated Channels: Open in response to changes in membrane potential.

Local Potential: Represents an initial change in membrane potential that can initiate an action potential if strong enough.
Action Potential: Characterized by a rapid, all-or-nothing response that propagates along the axon, involving depolarization and repolarization phases.

Action potentials propagate along the axon and can occur via:
- Continuous Conduction: Typically occurs in unmyelinated axons.
- Saltatory Conduction: Takes place in myelinated axons, facilitating quicker signal transmission.

Action potentials trigger the release of neurotransmitters from presynaptic neurons into the synaptic cleft, influencing postsynaptic neurons' activity.

Characterized by progressive loss of motor control due to degeneration of dopamine-releasing neurons, adversely affecting both movement and mental health.